Not all games will utilize CrossfireX. Some frustratingly will not work well or at all...
Since you have not posted your other specs we have no idea of potential bottlenecks or low performance components.
Recommend you optimize your OS and use an ssd for your gaming applications.
FRAPS can give you some reference as to how your system is performing.
Be sure you have very good airflow when using Crossfire, especially overclocked. Monitor your gpu temps and bump up your gpu fans if necessary.
Experiment with the 3D Application Settings to determine best overall performance. A better "look" can be obtained by carefully adjusting variables in "My Digital Flat Panels" tab.
Depending on the game and your specific cpu, some benefit may be realized by a small OC to your processor.
Don't fiddle with your memory (RAM) settings.
Go into your motherboard utility and study it as well as your f motherboard manual.
Try to keep gpu temps under ~80C or so.